1. Field of the Invention
The invention relates to a solenoid valve, in particular, a pressure control valve, comprising an armature with which by means of a plunger the slide is movable against a counter force, or comprising an armature and a slide which can be moved against a counter force.
2. Description of the Related Art
In a known solenoid valve a plunger is fastened in the armature and forms the closing element of the valve in order to control the flow from a pressure connector connected to a pressure medium source to a connector which is connected to a tank or the low-pressure chamber. The armature separates two armature chambers from one another which are connected with one another by a channel which extends through the armature and the plunger. This prevents the deposition of dirt particles which could impair the function of the solenoid valve.
It is an object of the present invention to configure the solenoid valve of the aforementioned kind such that an optimal function of the valve is ensured.
In accordance with the present invention, this is achieved in that the plunger has a smaller cross-section than the piston surface of the slide cooperating therewith, wherein the slide has at least one hydraulic chamber which is connected with at least one work connector and is connectable with a pressure connector. According to another embodiment, this object is achieved in accordance with the present invention in that the slide is hydraulically suspended or tensioned by being loaded from one end by the supply pressure and from the other end by the return pressure.
With the first embodiment of the solenoid valve according to the present invention it is possible to control large cross-sectional surfaces on the slide with relatively small solenoids without requiring a pilot control with control oil loss. The hydraulic chamber of the slide is connected with the work connector. When the solenoid valve is supplied with current, the slide is moved by means of the armature and the plunger such that the work connector is connected with the pressure connector. The solenoid valve according to the invention can be used advantageously in automatic transmissions or CVT-type (continuously variable transmission) systems.
In the second embodiment of the solenoid valve according to the invention, the slide is always hydraulically suspended or pre-tensioned. The supply pressure of the hydraulic medium is applied on one end of the slide, while the slide is loaded on the other end by the return pressure. In accordance with the pressure difference, the slide is thus correspondingly adjusted to the pilot control pressure. The adjustment of the slide, even in the case of contamination and thus increased frictional forces, is optimal. As a result of the pressure reduction between the supply pressure and the maximum pilot control pressure, the solenoid valve according to the invention is optimally stabilized despite sufficiently high adjusting forces acting on the slide.